Mobile communications system and method for providing common channel coverage using beamforming antennas

ABSTRACT

Wireless mobile unit communication initiation is provided in a radio network that has a plurality of base stations, each providing wireless communication services in a respective geographic coverage. The wireless communication is established by first transmitting an omnidirectional sounding pulse from a wireless mobile unit. Information related to the detected sounding pulse is communicated to an interface by each base station detecting the sounding pulse. One of the base stations that detected the sounding pulse is selected for mobile unit communication based on the communicated information and directs a communication beam to the mobile unit to establish wireless communication. Alternatively, one or more of the base stations that detected the sounding pulse direct a communication beam to the mobile unit and the mobile unit selects unit the base station with which it is to establish wireless communication. Preferably, smart antennas, including directional beamforming capability, are employed by the base stations.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No.60/401,697, filed Aug. 7, 2002 which is incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to mobile communication systems. Moreparticularly, the present invention relates to wireless communicationsystems that supporting mobile unit communications and a method ofincreasing capacity through the use of base stations with beamforming or“smart” antennas.

BACKGROUND OF THE INVENTION

Wireless communication systems are well known in the art. Generally,such systems comprise communication stations which transmit and receivewireless communication signals between each other. Typically, basestations are provided which are capable of conducting wirelessconcurrent communications with a plurality of subscriber stationsgenerically known as wireless transmit/receive units (WTRUs), whichinclude mobile units. Generally, the term base station includes but isnot limited to a base station, Node-B, site controller, access point orother interfacing device in a wireless environment. The term WTRUincludes but is not limited to a user equipment, mobile station, fixedor mobile subscriber unit, pager, or any other type of device capable ofoperating in a wireless environment.

In Universal Mobile Telecommunications Systems (UMTS) as specified bythe Third Generation Partnership Project (3GPP), base stations arecalled Node Bs, subscriber stations are called User Equipments (UEs) andthe wireless CDMA (Code Division Multiple Access) interface between theNode Bs and UEs is known as the Uu interface.

A typical UMTS system architecture in accordance with current 3GPPspecifications is depicted in FIG. 1 a. The UMTS network architectureincludes a Core Network (CN) interconnected with a UMTS TerrestrialRadio Access Network (UTRAN) via an interface known as Iu which isdefined in detail in the current publicly available 3GPP specificationdocuments.

The UTRAN is configured to provide wireless telecommunication servicesto users through UEs via the Uu radio interface. The UTRAN has basestations, Node Bs, which collectively provide for the geographiccoverage for wireless communications with UEs. In the UTRAN, groups ofone or more Node Bs are connected to a Radio Network Controller (RNC)via an interface known as Iub in 3GPP. The UTRAN may have several groupsof Node Bs connected to different RNCs. Two RNCs are shown in theexample depicted in FIG. 1 a. Where more than one RNC is provided in aUTRAN, inter-RNC communication is performed via an Iur interface.

In existing systems, when a mobile unit is first turned on or traversesinto a region of multiple base station coverage, a determination must bemade as to which base station the mobile unit will be paired forconducting wireless communication. Depending upon system design, themobile unit, the communications network or the base stations willdetermine the pairing between each mobile unit and a base station.

In one type of configuration, a mobile unit monitors common signals fromall base stations that it receives and synchronizes itself to the basestation with the best quality of service signal (QoS). In such systems,a beacon signal radiated by each base station is an omnidirectional highpowered transmission that has a tendency to generate interference.

Smart antennas that include beamforming capability are widely regardedas a promising technology for enhancing capacity and/or coverage ofwireless radio access systems, such as 3GPP mobile communicationssystems. The distinguishing feature of a wireless radio access systememploying smart antennas is that a user can be spatially isolated. Radiotransmissions directed toward, or received from, a user are isolated insuch a way that to minimalize interference to or from other users. FIG.1 b illustrates a smart antenna of a Node B focused at a UE of a 3GPPsystem.

Wireless radio access systems, such as UMTSs that employ smart antennas,derive two-fold system-level benefits by using highly focuseddirectional antennas. First, the system capacity improves as a result ofthe reduction in generated interference. Second, the system coverageimproves, resulting in an enhanced link budget. The increase in radiocoverage from the use of smart antenna technology represents aparticularly attractive feature for wireless communications systems. Theapplication of smart antenna technology, including beamforming is ratherstraightforward once a radio link is established between a mobile and aradio access point to exchange information over a dedicated channel.

In addition to dedicated radio links, common channels are typicallyemployed in wireless radio access systems. Common channels areestablished for various purposes, such as: 1) allowing for the temporalor frequency synchronization of mobiles, for example, a 3GPP sharedsynchronization channel (SCH); 2) broadcasting of system informationthat is essential for registration to the network upon power-up, forexample on a 3GPP broad cast channel (BCH); and 3) paging of idle-modemobiles, for example on a 3GPP paging indicator channel (PICH), pagingchannel (PCH) and forward access channel (FACH).

In a statistical sense, the geographical coverage that is provided bydownlink common channels defines the coverage area of a base station,which in UMTS, is commonly referred to as a cell. More specifically, theservice area provided by a wireless radio access system is determinedfrom the coverage of common channels.

A significant increase in cell area covered by a wireless radio accesssystem using smart antenna technology is enabled by employing highlydirectional antennas that boost the gain of such systems. Directionalantenna gain is achievable when the position of an antenna can beestimated by its peer antenna, and vice versa. Such circumstances aregenerally fulfilled when a dedicated radio link is established between amobile and a radio access point.

The usage of smart antennas for the transmission and reception of commonchannels is not defined in wireless radio access systems existing 3GPPspecifications and the advantages resulting from the use of smartantenna technology have yet to be exploited for the transmission andreception of common channels. A reason for this is that coverage ofcommon channels, such as BCH and PICH must be guaranteed for allmobiles, including those for which the location is unknown. Morespecifically, a radio access network must ensure that all mobiles canreliably synchronize with the network, read broadcast information, andmonitor pages, to name a few. This complication results in wirelessradio access systems that transmit common channels using conventionalomni-directional antennas that cover entire cells or cell sectors.

In order to match the extended coverage of dedicated channels usingsmart antennas, the transmission power of downlink common channels maybe increased. However, an increase in transmission power by all radioaccess points, for example, base stations, also results in an increasein interference. Such a solution is ineffective in wireless radio accesssystems that are limited by interference. The present preferred solutiontakes advantage of smart antenna technology to extend coverage whileminimizing interference.

SUMMARY

The present invention makes use of smart antenna technology, includingbeamforming for a wireless radio access system. The functionality ofsmart antennas for radio links is preferably applied to common channels,resulting in a significant increase in cell coverage. An omnidirectionalsounding pulse is used in connection with initiating mobile unitwireless communications. The sounding pulse, a radio frequency (RF)signal with or without intelligence, should not be confused withconventional mobile unit uplink channels.

In one embodiment a radio network is provided that has a plurality ofbase stations, each providing wireless communication services in arespective geographic coverage area that may or may not overlap with thegeographic coverage areas of other of the base stations. An interface isconnected to the base stations.

A wireless communication is established by first transmitting anomnidirectional sounding pulse from a wireless mobile unit located in ageographic coverage area of at least one of the base stations.Information related to the detected sounding pulse is communicated tothe interface by each base station detecting the sounding pulse. One ofthe base stations that detected the sounding pulse is selected formobile unit communication based on the communicated information. Theselected base station directs a communication beam to the mobile unit toestablish wireless communication.

In one non-limiting example of the first embodiment, the radio networkis a UMTS Terrestrial Radio Access Network (UTRAN), each base station isa Node B, the interface is a Radio Network Controller (RNC) and themobile unit is a mobile User Equipment (UE). In such case, thecommunicating of related sounding pulse information is between Node Bsand the RNC via an Iub or a combination Iub/Iur interface via anotherRNC. The base station selection is preferably performed by the RNC byselecting a Node B and the communication established between theselected Node B and the UE is via a Uu interface.

Preferably, each base station has a selectively operable beamformingantenna. The establishment of a wireless communication then includesdetermining a relative location of the mobile unit with respect to thebeamforming antenna of the selected base station based on informationrelated to the detected sounding pulse. Accordingly, in directing of acommunication beam the selected base station's antenna is operated toform a communication beam covering a selected portion of the coveragearea serviced by the selected base station that encompasses the relativelocation of the mobile unit.

The formed communication beam preferably carries common channels. Insuch case, the selected base station's antenna is operated to form acommunication beam that encompasses the relative location of the mobileunit such that other mobile units with which the selected base stationis conducting wireless communication are also encompassed within theformed communication beam so that the formed beam provides commonchannel service to a plurality of mobile units.

If the mobile unit does not receive a directed communication beam from abase station within a predefined time period from its transmitting of anomnidirectional sounding pulse, the communication initiation aspreferably restarted. Accordingly, the mobile unit is configured totransmit an omnidirectional sounding pulse to initiate communicationwith a base station and to transmit a subsequent sounding pulse whichmay be of increased power if a communication beam from a base stationthat detected a sounding pulse is not established.

Also, the mobile units are preferably configured to monitor the powerlevel of a communication with a base station and to repeating thecommunication initiation if the monitored power level falls below apredefined level. Additionally, the mobile units can be configured totransmit a series of omnidirectional sounding pulses of increasing powerto initiate communication with a base station.

An omnidirectional sounding pulse may be transmitted from each of aplurality of mobile units. In such case, information related to eachdistinguishable sounding pulse from each respective mobile unit detectedby a base station is communicated to a respective selecting interface.Each respective interface selects a base station for each respectivemobile unit communication based on the information related to thedistinguishable detected sounding pulse of the respective mobile unitfrom each base station that detected a distinguishable sounding pulse ofthe respective mobile unit. For each respective mobile unit for which atleast one base station received a distinguishable sounding pulse, acommunication beam from the respective selected base station is directedto the mobile unit to establish wireless communication.

Preferably, the formed communication beams carry common channels. Insome instances, a first base station is selected for communication witha first mobile unit and is also selected for communication with a secondmobile unit. The first base station's antenna is then operated to form acommunication beam that encompasses the relative location of both thefirst and second mobile units so that the formed beam provides commonchannel service to both first and second mobile units. In otherinstances a first base station is selected for communication with afirst mobile unit by a first selected interface and a second basestation is selected for communication with a second mobile unit by asecond selected interface.

When at least one base station receives the sounding pulse, measurementscan be made to determine a received power level and an estimate of theangle of arrival to the mobile unit. This information from one or morebase stations can be used to determine the mobile unit's relativelocation and to accordingly direct a communication beam toward themobile unit.

In a second embodiment, the mobile unit selects the base station withwhich it will establish wireless communication. As in the firstembodiment, an omnidirectional sounding pulse is transmitted from themobile unit located in a geographic coverage area of at least one of thebase stations. A communication beam is directed from base stationsdetecting the sounding pulse towards the mobile unit. One of the basestations that detected the sounding pulse is then selected based on thecommunication beams received by the mobile unit. A wirelesscommunication is then established between the selected base station andthe mobile unit.

The implementing radio network can have a controlling interfaceconnected to the base stations. In such case, the information related tothe detected sounding pulse can be communicated to the interface by eachbase station detecting the sounding pulse. One or more of the basestations that detected the sounding pulse can then be chosen based onthe communicated information so that only the chosen base stationsdirect a communication beam to the mobile unit. In this way the radioaccess network can selectively limit the selection made by the mobileunit.

A preferred mobile includes a transmitter configured to transmit anomnidirectional sounding pulse and a receiver for receivingcommunication beams from base stations that detected a sounding pulsetransmitted by the mobile unit. To implement the second embodiment, themobile unit includes a processor configured to select a base stationwith which to establishing a wireless communication based oncommunication beams received by the mobile unit from base stations thatdetected a sounding pulse transmitted by the mobile unit.

Each mobile unit can be equipped with a global positioning system (GPS).In such case, the mobile units are preferably configured to transmit ofan omnidirectional sounding pulse that includes mobile unit locationinformation determined by its GPS. The mobile units can also beconfigured to transmit of an omnidirectional sounding pulse thatincludes mobile unit identification information.

Other objects and advantages of the present invention will be apparentto those skilled in the art from the following detailed description andrelate drawings.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 a depicts a typical UMTS system architecture in accordance withcurrent 3GPP specifications.

FIG. 1 b illustrates a smart antenna of a Node B focused at a UE of a3GPP system.

FIG. 1 c illustrates a UE traveling through the cells covered by anetwork of node B base stations of a 3GPP system that employ smartantennas.

FIG. 2 is a flow diagram of a base station selection procedure inaccordance with an embodiment of the present invention.

FIG. 3 is a flow diagram of a base station selection procedure variationin accordance with an embodiment of the present invention.

FIG. 4 is a flow diagram of a reselection procedure in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described with reference to the drawing figureswherein like numerals represent like elements throughout. The presentinvention can be applied to some or all of a systems' downlink commonchannels. For reason of simplicity, the invention as applied to a UMTSsystem for downlink common channels is described herein. However, theproposed invention is applicable in any wireless system.

The present invention provides a wireless radio access network havingnetworked base stations with an improved base station selectionmechanism for mobile units, i.e. mobile WTRUs, as they enter and/ortravel through the respective areas of geographic coverage provided bythe respective base stations. Such mobile units, for example the UEsillustrated in FIG. 1 a, generally include a transmitter, a receiver anda communication signal processor. The network preferably includes sometype of base station interface that makes the selection. Such aninterface for node Bs of a 3GPP network is a Radio Network Controller(RNC). However, an alternative embodiment provides for self-selection bythe mobile unit.

In lieu of providing complete uniform coverage throughout an entire cellor cell sector, a base station selectively directs at least some, butpreferably all, downlink common channels toward individual mobile unitsusing smart antenna technology, including beamforming. FIG. 1 billustrates such coverage in a 3GPP system by a node B for a mobile unitUE1 traveling a cell indicated in phantom. Preferably, coverage by abase station of a downlink common channel or beacon channel matches thatof dedicated channels using smart antennas.

A pattern of mutually exclusive cells can be mapped to denote theoverall coverage area of a wireless radio access network as illustratedin phantom in FIG. 1 c. However, the actual geographic coverage areacapable of being serviced by each base station normally extends beyondthe nominal cell mapping and overlaps with the actual geographiccoverage area of neighboring base stations. For, example in FIG. 1 c,the mobile unit UE is depicted as being capable of being serviced by atleast any of base stations BS₁, BS₂, or BS₄.

FIG. 2 is a flow diagram of a base station selection procedure inaccordance with an embodiment of the present invention. In a first step202, a mobile unit emits a sounding pulse in a using an omni directionalantenna to produce a uniformly radiated radio frequency (RF) pattern.Each base station that receives the sounding pulse, communicates thatinformation to a Radio Network Controller (RAN) as indicated in step204. For example, a sounding pulse emitted by mobile unit UE in FIG. 1 cwould most likely be received by base stations BS₂ and BS₄, but may alsobe received by base station BS₁ and possibly base stations BS₆ and BS₇as well.

The receiving base stations may or may not be controlled by the sameRNC. Where more that one RNC is involved, preferably the one that firstreceives a communication from one of its associated node B base stationsbecomes the deciding RNC and has the reception of the sounding pulseinformation conveyed to it by the RNC(s) associated with the other basestation(s) that receive the sounding pulse such as via a standard Iurinterface as illustrated in FIG. 1 a. Where a base station is in anotherUTRAN, communication to the deciding RNC can be made via the corenetwork of an existing 3GPP system.

The RAN selects one of the pulse receiving base stations and determinesthe direction from the selected base station to the mobile unit asreflected in step 206. The selection decision is preferably based on thestrength of the received signal. Where more than one base stationreceives the sounding pulse above a selected minimum strength, otherstandard quality of service Qos criteria can be compared in theselection process. Also, overall network traffic may be considered inthe selection decision such as disclosed in U.S. patent application Ser.No. 10/305,595 owned by the assignee of the present invention.

Where the deciding RNC is not the RNC directly associated with theselected base station, the selected base station's RNC can be used todetermine the direction from the selected base station to the mobileunit. However, where overall network traffic is being evaluated theRNC(s) can communicate all of the data to the core network and the corenetwork can be utilized to assist in or make the base station selection.Such alternatives can be triggered when the communication traffic withrespect to an RNC or UTRAN reach certain specified minimum levels. Asintimated by FIG. 1 c, even though base stations BS₂ and BS₄, are closerto mobile unit UE, base station BS₁ can possibly be selected based onQos and overall network traffic considerations.

As indicated in step 208, once selected, the selected base stationdirects its transmission of downlink common channels towards the mobileunit as shown in FIG. 1 b. The base station is preferably provided witha beamforming antenna for this purpose and the direction of the beam ispreferably base on an estimate of the mobile unit's location.Directional antennas, phased array antennas or other types of antennasystems can be provided so that a beam from a base station antenna fortransmission and/or reception covers a particular geographic area of aspecific shape and size. The location estimate can be derived in anumber of ways, but is preferably based upon information related toreception of the sounding pulse by one or more base stations.Quantitative measurements of beam strength and/or angle of receptionfrom one or more base stations can be used in a conventional manner tocalculate a relative mobile unit location. In a 3GPP type system, thismay be done at either the RNC or the Node B. Alternatively, geolocationdata may be attached to the sounding pulse by the mobile unit and arelative position determined by comparison with the known location ofthe selected base station's antenna. The mobile unit may be equippedwith a Global Positioning System (GPS) for this purpose.

The sounding pulse is a physical signal that is preferably transmittedusing an isotropic antenna, which is an antenna that radiates orreceives equally in all directions. The form of the sounding pulse ispreferably dependent on the radio access technology. For example, inCDMA-based systems, a very short duration burst spanning multiple chips,a short chip sequence, can represent the sounding pulse.

The timing for the sounding pulse depends on the implementation andrealization of the physical signal, which depends on radio accesstechnology. Each wireless communication medium requires a differentpulse timing structure. For example, a FDD-CDMA sounding pulse would bedifferent than a TDD-CDMA sounding pulse.

The physical signal that defines the sounding pulse itself may berealized with an Aloha or slotted Aloha technique. In an Aloha-liketechnique, the mobile unit simply transmits the sounding pulse burstwhenever it wants to. There are no timing restrictions in the Aloha-likesystem. If the mobile unit does not get a response from a base station,this is considered a “connect” failure. A back-off procedure is thenimplemented. This procedure essentially retries to connect after themobile unit waits a random amount of time until retransmitting.

In the slotted Aloha-like technique, the mobile unit transmits thesounding pulse at specific timeslots. This technique requires some sortof master timing. In case of failure, the back-off procedure correspondsto a mobile unit waiting a random number of timeslots until which themobile unit retransmits.

In some situations, multiple mobile units may pulse at the same time toacquire the attention of the same RAN. When this occurs and the Node Bscan differentiate the signals from both mobile units, the RAN selectsnode Bs to direct common channels towards each mobile unit. If the NodeBs cannot differentiate the signals from each mobile unit, the RANcannot make a proper Node B selection to direct the common channelstoward each mobile unit. In this case, the selection preferably awaitsthe next pulse transmitted by each mobile unit. To ensure thatsubsequent pulses from these mobile units do not collide, a preferredback-off procedure for the mobile units includes waiting a random amountof time before retransmitting a sounding pulse, thus avoiding anothercollision. Successive pulses may be at increased power as discussed inthe variation below.

A variation of the procedure illustrated in FIG. 2 is set forth in FIG.3. Once the mobile unit enters a network service area, step 302, itemits a first sounding pulse at a low power, step 304. However, insteadof a single pulse, the mobile unit emits a series of pulses andgradually steps up the transmission power during the emission of theseries of sounding pulses, step 306. Preferably, each successive pulseis transmitted with a greater power than its immediate predecessorpulse.

One or more base stations which each detect at least one sounding pulsecommunicates its sounding pulse reception information to a RAN, step308. The RAN selects one of the base stations and calculates therelative location of the mobile unit, step 310. The selected basestation then directs one or more down link common channels to the mobileunit using smart antenna technology, step 312. The mobile unit thenreceives the down link channels and can then commences communicationswith another unit via the selected base station, step 314.

In either embodiment, upon detection of a sounding pulse, the radioaccess network (RAN) preferably uses measurements performed on thesounding pulse to subsequently direct the selected base station'stransmission of one or many downlink common channels using a smartantenna. For example, the received signal power of the sounding pulseand the angle of arrival of the signal relative to a single base stationcan be used to determine the position of the mobile unit and thedirection towards which common channels should be radiated using smartantennas. However, the RNC can correlate data received from all of thebase stations that communicate reception of the sounding pulse to make amore accurate calculation of the mobile unit's geographic location.

A mobile unit preferably makes its presence known to a RAN upon power-upor when entering a UTRAN service area. Accordingly, the base stationsmust listen for sounding pulses at regular time intervals orcontinuously in order to detect the emergence of new mobile units. Inaddition, in order to maintain a relationship with a particular basestation, mobile units that are camped out on a particular base station,i.e. not actively conducting communications, preferably scheduleperiodic pulses to ensure tracking of the location of the mobile unit socommunications directed to such mobile unit can be promptly connected.

In order to facilitate the transmission and detection of the soundingpulse, certain downlink common channels providing timing informationwith respect to access opportunities for the uplink sounding pulse maybe transmitted using omnidirectional antennas. However, this ispreferably only performed if the coverage of such synchronizationchannels can be assured without sacrificing downlink capacity.

In a variation of the FIG. 3 embodiment, a series of sounding pulses aresent according to a power ramp-up procedure as follows. A mobile unittransmits an initial sounding pulse at a low power level as in step 304.After a period of time without reception of a reply from a base station,the mobile unit will step up the transmitted power and retry itssounding pulse. The procedure is repeated until a sufficient downlinkcommunication from a base station is received. In other words, step 306is skipped, or stopped, once steps 308, 310 and 312 are performed. Theamount of time until the transmission of a “stepped-up” higher powersounding pulse can either be fixed or determined from a random back-offprocess performed by the mobile unit. Additionally, the amount of powerincrease for each step can also be fixed or variable.

In addition to or as an alternative to transmitting a sounding pulseupon entry into a service area, the mobile unit can be configured totransmit a sounding pulse when the received signal code power (RSCP) ofone or more selected common channels falls below a certain thresholdlevel. Also, once the radio access network has determined the locationof the mobile unit, registration and authentication information ispreferably exchanged between the network and the mobile unit. Networkregistration is preferably performed using conventional protocols as incurrent wireless systems.

While the invention relates to the usage of smart antennas on thedownlink of the common channels, uplink registration and authenticationinformation is not required to be transmitted using smart antennas.During further idle mode operation, which includes monitoring of pages,updates of system and broadcast information, network synchronization andother procedures are ensured through a mechanism that employs soundingpulses to track displaced mobiles. A displaced mobile is a mobile unitthat has moved out from beneath the penumbra of the focused antenna ofthe base station that had been selected for communication with themobile unit.

As in discontinuous reception for conventional UMTS systems, anidle-mode mobile unit must “wake-up” and acquire one or many commonchannels such as a paging channels or updates to system information on abroadcast channel (BCH). If the received power on desired commonchannel(s) is insufficient, the mobile unit can be configured totransmit a sounding pulse such that the radio access network canredirect the transmission of common channels using a base station'ssmart antenna.

Another application is realized for mobile units which employ aconventional DRX cycle. A DRX cycle is a mode a mobile unit reverts towhen it loses contact with the network. If a mobile unit becomesdisconnected from the network, the mobile unit will preferablyperiodically transmit a sounding pulse every DRX cycle prior to theacquisition of common channels in accordance with the invention asdescribed above.

As a mobile unit traverses through a coverage area and more specificallyupon leaving the coverage area of a given cell, there is a need forreselection of an appropriate base station for facilitatingcommunications with the mobile unit. This can be done in accordance withthe process described above using a base station interface device suchas a 3GPP RNC. As an alternative, a mobile unit can be configured to becapable of selecting or reselecting a base station itself.

While a mobile unit self-selection is equally applicable for initiatingwireless communication, a mobile unit self-selecting reselectionprocedure in accordance with the second embodiment of the presentinvention is set forth in FIG. 4. In the case of reselection, the mobileunit monitors the received power of a downlink common channeltransmitted by a currently selected base station to determine if itdrops below a pre-selected threshold, step 402. When the threshold ispassed, the mobile unit transmits a sounding pulse, step 404. Uponreception of the sounding pulse, neighboring base stations that receivethe pulse direct the transmission of downlink common channels toward themobile unit, step 406.

FIG. 1 c represents the case where base station BS₁ was previouslyselected for servicing communications for mobile unit UE which hasemitted a sounding pulse after moving out of the nominal cell servicedby that base station. The figure illustrates base stations BS₂ and BS₄,having received the pulse, directing downlink common channels, forexample a beacon channel, toward mobile unit UE. In this alternateembodiment, the mobile unit selects a base station based upon acomparison of the reception of downlink common channels from suchneighboring base stations, step 408. Preferably, a cell registrationprocess is then performed via the newly selected base station toproperly redesignate the mobile units location with respect to thenetwork, step 410.

The radio access network can control which cell a mobile unit selects byvirtue of its control of the base station transmissions. Upon receptionof the sounding pulse from multiple base stations, a RNC can estimatethe location of the mobile unit using triangulation techniques andmeasurements from all base stations on the sounding pulse. The radionetwork controller can utilizes the location of the mobile unit todirect the transmission of common channels from only one base station,i.e. the one to which the RNC chooses that the mobile unit shouldselect. This type of control is particularly useful when evaluatingoverall network usage and capacity of particular node Bs so in order toprovide a better utilization of network resources at a given time.

The sounding pulses can be generated at a frequency outside normaluplink and downlink telecom frequencies, thereby alleviating frequencycongestion. For example, in a current deployment of CDMA, the mobileunits are normally assigned channels at least 1.25 MHz apart, providingabout 42 channels under current frequency allocation scheme. Typically,the uplink transmit frequency is 45 MHz lower than the downlink transmitfrequency. The sounding pulses are preferably then assigned to afrequency in close proximity to the uplink or downlink, but not on thesame frequency as either the uplink or downlink transmissions.

Normally the sounding pulse is preferably a simple short signal,containing no specific information, but optionally the sounding pulsecan contain identification information from the mobile unit. With suchinformation, the base stations can readily determine and distinguishbetween pulses concurrently received from more than one mobile unit.This information can indicate the reason for which the mobile wants toconnect to the network. For example, the mobile unit may want to simplyregister with the network or it may wish to set up a call.

Other variations and alternatives will be apparent to those skilled inthe art and are considered to be within the scope of the presentinvention.

1. A method for use in wireless communication at a base station, themethod comprising: transmitting information to a wireless/transmitreceive unit (WTRU), the information indicating an assignment ofperiodic time intervals to transmit sounding signals; in response to thetransmitted information, detecting sounding signals from the WTRU in theassigned periodic time intervals, wherein the sounding signals from theWTRU are distinguishable from sounding signals from other WTRUs, and thesounding signals are received from the WTRU in the assigned periodictime intervals on a condition that the WTRU is not transmitting data inthe time interval; and using a selectively operable beamforming antennaarray to direct downlink channel transmissions toward a relativelocation of the WTRU based on the received detected sounding signals. 2.The method of claim 1, wherein the sounding signals are sounding pulses.3. A base station comprising: a selectively operable beamforming antennaarray; a transmitter configured to transmit information to awireless/transmit receive unit (WTRU), the information indicating anassignment of periodic time intervals to transmit sounding signals; areceiver, in response to the transmitted information, configured todetect sounding signals from the WTRU in the assigned periodic timeintervals, wherein the sounding signals from the WTRU aredistinguishable from sounding signals from other WTRUs, and the soundingsignals are received from the WTRU in the assigned periodic timeintervals on a condition that the WTRU is not transmitting data in thetime interval; and a transmitter configured to selectively operate thebeamforming antenna array to direct downlink channel transmissionstoward a relative location of the WTRU based on the received detectedsounding signals.
 4. The base station of claim 3, wherein the soundingsignals are sounding pulses.
 5. A method for use in a wirelesstransmit/receive unit (WTRU), the method comprising: receivinginformation by the WTRU from a base station, the information indicatingan assignment of periodic time intervals to transmit sounding signals;in response to the received information, transmitting sounding signalsby the WTRU to the base station in the assigned periodic time intervals,wherein the sounding signals from the WTRU are distinguishable fromsounding signals from other WTRUs, and the WTRU transmits the soundingsignals in the assigned periodic time intervals on a condition that theWTRU is not transmitting data in the time interval; and receivingbeamformed downlink channel transmissions by the WTRU from the basestation based on the sounding signals.
 6. The method of claim 5, whereinthe sounding signals are sounding pulses.
 7. The method of claim 5,wherein the WTRU receives substantially simultaneous beamformedtransmissions from a plurality of base stations in response to thesounding signals.
 8. A wireless transmit/receive unit (WTRU) comprising:a receiver configured to receive information from a base station, theinformation indicating an assignment of periodic time intervals totransmit sounding signals; a transmitter configured to transmit soundingsignals to the base station in the assigned periodic time intervals inresponse to the received information, wherein the sounding signals aredistinguishable from sounding signals from other WTRUs, and the soundingsignals are transmitted in the assigned periodic time intervals on acondition that the WTRU is not transmitting data in the time interval;and wherein the receiver is further configured to receive beamformeddownlink channel transmissions from the base station based on thesounding signals.
 9. The WTRU of claim 8, wherein the sounding signalsare sounding pulses.
 10. The WTRU of claim 8, wherein the receiver isfurther configured to receive substantially simultaneous beamformedtransmissions from a plurality of base stations in response to thesounding signals.
 11. A method for use in a wireless communicationsystem using beamforming, the method comprising: transmittinginformation by a first base station to a wireless transmit/receive unit(WTRU), the information indicating an assignment of periodic timeintervals to transmit sounding signals; in response to the transmittedinformation, detecting, by a plurality of base stations including thefirst base station, sounding signals from the WTRU in the assignedperiodic time intervals, wherein the sounding signals from the WTRU aredistinguishable from sounding signals from other WTRUs, and the soundingsignals are received from the WTRU in the assigned periodic timeintervals on a condition that the WTRU is not transmitting data in thetime interval; and each of the plurality of base stations using aselectively operable beamforming antenna array to substantiallysimultaneously direct downlink channel transmissions toward a relativelocation of the WTRU based on the received detected sounding signals.